High Wind in California, November 17, 2020

Area Forecast Discussion
National Weather Service Medford OR
858 AM PST Tue Nov 17 2020

.UPDATE...Timing of precipitation was sped up a bit this
morning...as current conditions had moisture further east than
originally forecast. There is still quite a bit of uncertainty
when it comes to the wind forecast through noon. In the past
hour...wind gusts between 45 and 65 mph were present across the
higher elevations...however the winds hadn't materialized across
most of the valley locations. The cold front continues to make its
way east through the forecast area...which will likely mix down
some of the stronger winds. We did not adjust winds...kept them as
is...however confidence is medium to low that we will reach the
magnitude as originally forecast...especially for the valley
locations.

Otherwise...current forecast looks to be on track...with unsettled
weather through at least Thursday morning.

&&

.PREV DISCUSSION... /Issued 300 AM PST Tue Nov 17 2020/

DISCUSSION...A rapidly deepening cyclone is making its way north
along 130W and will move inland into Vancouver Island/British
Columbia later this morning. Very strong winds associated with
this low pressure will be felt across the forecast area this
morning and afternoon. Winds have already increased with gusts of
40 to 50 mph are already occurring along the coast, the higher
terrain and in the Shasta Valley with gusts of 20 to 30 mph common
across the East Side. It's been fairly calm in the Rogue Valley
so far, however, that is changing. At 1 am the Medford Airport was
44 degrees with a half mile visibility in fog. By 130 am, visibility
was clear and the temperature warmed to 60 degrees thanks to
southeast winds increasing in the valley. Winds will continue to
increase across the area as the morning progresses and pressure
gradients tighten. Guidance still indicates the RDD-MFR gradients
peaking at 7-9 mb with 700 mb winds of 70-80 kts moving through
the area this morning. The forecast remains on track for a
significant wind event and a plethora of wind headlines are in
place for this at NPWMFR. Winds will remain strong through early
afternoon, then gradually diminish by this evening.

The cold front associated with this low will move into the coast
early this morning, then move inland to east of the Cascades by
early afternoon. Most areas will see another good round of
precipitation with this front. Expect 1" to 3" for the typical
winners in terms of precipitation amounts (Coast
Ranges/Cascades/Siskiyous), but also in the Mt. Shasta region, where
850-700mb flow is maximized for a 6-9 hour period. Since snow levels
will be mostly 5500 feet and above for this front, we aren't
anticipating winter weather impacts. Downslope flow in the
Rogue/Shasta Valleys will keep precipitation totals lower with
generally 0.25 of an inch or less -- with a similar story over the
East Side.

There won't be much break in the weather once this front passes
as multiple shortwaves follow Wednesday into Thursday. Snow levels
will lower late tonight down to 4500 ft ahead of the first
shortwave expected Wednesday morning and afternoon. Another round
of beneficial precipitation is expected and there could be some
snow impacts for the Cascades Wednesday. Snow levels are expected
to remain above the major passes Wednesday, however, snow levels
could lower down to Siskiyou Summit late Wednesday night into
Thursday. Precipitation amounts will be considerably less for with
the Thursday shortwave, so any snow impacts should be minimal.

Expect a break in the weather for Friday and Saturday as drier air
and upper level ridging moves into the region. With plenty of recent
moisture, valley fog will be common across the area Thursday and
Friday nights. Fog will likely linger well into the afternoon hours
under this pattern, leading to cool days for most west side valleys.
Where fog doesn't develop expect some cold overnight temperatures
under clear skies. This break doesn't last too long, however, as
another front is expected late Saturday into Sunday with more fronts
to follow through the extended period. /BR-y

.AVIATION...For the 17/12Z TAFS...Over the coastal waters and along
the coast...It will be very windy this morning with widespread
turbulence and low level wind shear as a front moves onshore. Wind-
related conditions will improve after the front moves inland. Areas
of MVFR cigs/vsbys with higher terrain obscured will become
widespread Tuesday evening, with the lower conditions prevailing
into Wednesday morning.

Inland...It will be very windy into the afternoon with widespread
turbulence and low level wind shear as a front approaches the
area. Wind-related conditions will improve after the front moves
inland. Otherwise, mostly VFR conditions will prevail initially, but
there will be extensive obscuration of higher terrain. Areas of MVFR
cigs will develop Tuesday night, persisting into Wednesday morning.

&&

.MARINE...Updated 840 AM PST Tuesday 17 Nov 2020...Storm force
winds will lower some to gales later this morning while seas remain
very steep and hazardous through the day and into Wednesday.
Additional fronts will move onshore Wednesday into Thursday, but
they will be weaker than the system today. Seas lower to below 10
feet by Thursday afternoon. There will be a break in the frontal
activity Friday into Saturday, then another front will move onshore
Saturday night into Sunday. Small Craft Advisory conditions could
accompany this front. Keene

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning until 7 PM PST this evening for ORZ030-031.
     Wind Advisory until 7 PM PST this evening for ORZ030-031.
     High Wind Warning until 1 PM PST this afternoon for ORZ021-022.
     Wind Advisory until 1 PM PST this afternoon for ORZ023>025.
     High Wind Warning until 7 PM PST this evening for ORZ027-028.
     Wind Advisory until 7 PM PST this evening for ORZ029.
     High Wind Warning until 4 PM PST this afternoon for ORZ026.
     Wind Advisory until 4 PM PST this afternoon for ORZ026.

CA...High Wind Warning until 7 PM PST this evening for CAZ085.
     Wind Advisory until 7 PM PST this evening for CAZ085.
     High Wind Warning until 7 PM PST this evening for CAZ082-083.
     Wind Advisory until 7 PM PST this evening for CAZ084.
     High Wind Warning until 4 PM PST this afternoon for CAZ081.

Pacific Coastal Waters...Storm Warning until 10 AM PST this morning for
     PZZ350-356-370-376.
     Gale Warning until 1 PM PST this afternoon for PZZ350-356.
     Hazardous Seas Warning from 1 PM this afternoon to 10 PM PST
     Wednesday for PZZ350-356-370-376.
     Gale Warning until 1 PM PST this afternoon for PZZ370-376.